As having small and thin sizes, disk drives, such as a magnetic disk drive, have been used in mobile devices, and accordingly, have opportunities to receive excessive impact due to strong vibration, dropping, or collision. When receiving such a strong external impact, a magnetic disk drive including a head support device having a floating head exhibits a phenomenon in which a slider jumps off the magnetic recording medium due to unbalance between the floating of the slider caused by an airflow generated by rotation of the magnetic recording medium and an urging force caused by the head support device for urging the slider toward the magnetic recording medium.
At this moment, the slider may be hit the magnetic recording medium, providing magnetic or mechanical damage to the magnetic recording medium or to a magnetic head mounted on the slider. In order to prevent such problems, a self-balancing type head support device is proposed that satisfies demands physically incompatible: a large load on the slider, high flexibility, and additionally high rigidity of the structure, and that has a feature of strong impact resistance. The above-mentioned conventional structure is disclosed in Japanese Patent No. 3374846 and Japanese Patent Laid-Open Publication No. 2004-62936.
Hereinafter, the structure of a self-balancing type head support device in a magnetic disk drive, such as a hard disk drive, as a head support device of a disk drive including a conventional floating head will be described briefly with reference to FIGS. 11 and 12. FIG. 11 is a side view of the conventional self-balancing head support device. FIG. 12 is an exploded perspective view of the conventional self-balancing head support device.
As shown in FIGS. 11 and 12, slider 111 having a magnetic head (not shown) on a bottom surface thereof is mounted onto one end of support arm 112. Another end of support arm 112 is attached fixedly to one end of plate spring 113. Another end of plate spring 113 contacts pivot bearing 115 through spring fixing member 114. Bearing 117 is a rotation center for rotating support arm 112 in the radial direction of magnetic recording medium 116 Flange 117a and nut 118 of bearing 117 cramp plate spring 113 and spring fixing member 114. Thus, another end of plate spring 113 is fixed to pivot bearing 115.
Spring fixing member 114 is cramped through projection 119a having a half-annular shape. Projection 119a has a shape substantially identical to that of a portion of spring fixing member 114 contacting spring fixing member 114, and is provided on hollow collar 119. This arrangement allows support arm 112 to be retained elastically on pivot bearing 115 through plate spring 113.
Pivot bearing 115 has a pair of tops 115a and 115b. Tops 115a and 115b contact support arm 112 at contact points Pa and Pb, respectively. The one end of support arm 112 is urged toward magnetic recording medium 116 by an elastic force of plate spring 113. At this moment, a compression stress occurs at contact points Pa and Pb. Tops 115a and 115b of pivot bearing 115 are perpendicular to a longitudinal direction of support arm 112 and to a rotation center axis about which support arm 112 rotates in the radial direction of magnetic recording medium 116. Tops 115a and 115b contact support arm 112 on the line passing through the rotation center axis.
The gravity center of a portion retained by plate spring 113 matches the gravity center of support arm 112 having voice coil 120 and coil holder 121 attached thereto when rotated by a voice coil motor. The head support device is designed so that this gravity center matches substantially with an intersecting point between the rotation axis (not shown) in the radial direction of support arm 112 and the rotation axis perpendicular to a recording surface of magnetic recording medium 116. In other words, the head support device is designed so that the gravity center matches substantively with middle point P (not shown) of the line connected between contact points Pa and Pb at which support arm 112 contacts tops 115a and 115b, respectively. This structure provides a stable self-balancing type head support device having large impact resistance against an external impact.
However, in the conventional self-balancing head type support device, a small gap exists between a hollow portion of collar 119 and cylinder portion 117c of bearing 117 fitting the hollow portion. The small gap provided between collar 119 and bearing 117 may cause a contact position of projection 119a of collar 119 contacting plate spring 113 to vary when plate spring 113 is cramped by fitting thread portion 117b of bearing 117 to nut 118. This variation may change the effective length of a spring portion of plate spring 113, and thus, may change its spring repulsive force, causing a load on magnetic recording medium 116 to vary.
Similarly to this, regarding the fitting between pivot bearing 115 and cylinder portion 117c of bearing 117, the small gap may cause the positional relationship between support arm 112, pivot bearing 115, and bearing 117 to vary. In other words, contact points Pa and Pb contacting tops 115a and 115b of pivot bearing 115 may vary. Similarly to the variation of the contact point of projection 119a of collar 119, a load due to a compression stress toward the magnetic recording medium 116 may vary as a reactive force due to deformation of plate spring 113.